The Cremer's impedance theoretical framework has been used for years to optimally design acoustic liners for the aeronautic industry, such as honeycomb liners. This passive mean of sound absorption, which consists in rather thin (a few centimeters) honeycomb-shaped cavities glued between a perforated sheet and a rigid backwall, has several downsides: an optimal acoustic absorption can only be achieved over a limited bandwidth, centered around one (eventually two) prescribed central frequency. Their performance at low frequencies is also limited by their size, owing to the "quarter-wavelength rule". In this paper, we propose a fully tunable active liner based on electrodynamic resonators, employing loudspeaker membranes as sound absorbers, and an active control framework allowing modifying their acoustic impedance over a wide frequency band. An optimization of these active absorbers is achieved by considering the theoretical framework of the generalized Snell-Descartes law, which accounts for impedance gratings over an interface. Through this formalism, it is possible to devise a wave conversion strategy within an active acoustic liner in order to absorb multimodal sound propagation inside a rigid duct, improving the noise attenuation performance of the liner over an extended bandwidth.
